Quartz glass blank for an optical component and its utilization

ABSTRACT

The present invention concerns a quartz glass blank for an optical component for the transmission of ultraviolet radiation of a wave length of 250 nm and under, as well as its utilization in microlilthography in connection with ultraviolet radiation of a wavelength of 250 nm and under. Such quartz glass blank is to have low induced absorption, while being optimized in respect of compaction and de-compaction. The quartz glass blank according to the invention has the following properties:  
     A glass structure essentially free of oxygen defect sites;  
     a H 2  content in the range of 3×10 17  molecules/cm 3  to 2.0×10 18  molecules/cm 3 ;  
     an OH content in the range of 500 weight ppm to 1000 weight ppm;  
     a SiH group content of less than 2×10 17  molecules/cm 3 ;  
     a chlorine content in the range of 60 weight ppm to 120 weight ppm;  
     a refractive index inhomogeneity, Δn, of less than 2 ppm; and  
     a stress birefringence of less than 2 nm/cm.  
     For utilization according to the invention, the quartz glass blank—in respect of its minimum and maximum hydrogen content, C H2min  and C H2max , as well as its OH content C OH —is in accordance with the scaling laws (2), (3) and (4), with P standing for the pulse number and ε for the energy density:  
       C   H2min  [molecules/cm 3 ]=1.0×10 8 ε 2   P   ( 2 ),  
       C   H2max  [molecules/cm 3 ]=2×10 19 ε  ( 3 ),  
       C   OH  [weight ppm]=1700ε [mJ/cm 2 ] 0.4 ±50  ( 4 ).

[0001] This invention concerns a quartz glass blank for an optical component for transmission of ultra-violet radiation of a wavelength of 250 nm and under.

[0002] Furthermore, the invention concerns the utilization of a quartz glass blank for the manufacture of a component for application in microlithography in connection with ultra-violet radiation of a wavelength of 250 nm and under.

[0003] Optical components of quartz glass are used above all for the transmission of high-energy ultraviolet laser radiation, for example as optical fibers or in the form of optic illumination devices in microlithography systems for the manufacture of large-scale integrated circuits in semiconductor chips. The illumination systems of modern microlithography systems are equipped with excimer lasers radiating high-energy pulsed UV radiation of a wavelength of 248 nm (KrF laser) or of 193 nm (ArF laser).

[0004] In optical components of synthetic quartz glass, short-wave UV radiation can cause damages resulting in absorptions. Type and extent of the damages and the absorption induced by them depend not only on the radiation conditions, but also on the quality of the respective quartz glass which is primarily defined by structural characteristics, as e.g. density, gradient of the index of refraction, and homogeneity, as well as by the chemical composition.

[0005] A model formula describes the relation between radiation conditions, material factors, and the induced absorption α_(in) as follows:

α_(in) =a×ε ^(b) ×P  (1);

[0006] here, a and b are the material factors, while ε and P stand for energy density respectively pulse number.

[0007] Accordingly, the number of the induced structural damages and the absorption induced by them depend on the number of the laser pulses taking effect and on their energy density, as well as on material factors.

[0008] The effect of the chemical composition of the quartz glass on damage behavior at radiation with high-energy UV light is for example described in EP-A1 401 845. According to the named patent, a quartz glass of high purity having an OH content ranging from 100 to approx. 1000 weight ppm, together with a hydrogen concentration of at least 5×10¹⁶ molecules per cm³ (in relation to the volume of the quartz glass), shows high radiation resistance. Moreover, the known synthetic quartz glass has a stress birefringence of under 5 nm/cm and is essentially free of oxygen defect sites.

[0009] Furthermore, EP-A1 401 845 describes methods for manufacture of synthetic quartz glass by flame hydrolysis of siliceous compounds. These compounds can be differentiated on the basis of the starting substances and the type of vitrification of the precipitated SiO₂ particles. In manufacture of synthetic quartz glass by flame hydrolysis, SiCl₄ is frequently used as a starting substance. Alternatively, other e.g. chlorine-free siliceous organic compounds are used, for example hydrosilicon or siloxane. In any case, SiO₂ particles are precipitated in layers on a rotating substrate. With a sufficiently high temperature on the surface of the substrate, direct vitrification of the SiO₂ particles occurs (“direct vitrification”). In the so-called “soot method”, however, the temperature during precipitation of the SiO₂ particles is kept so low that a porous soot body is formed in which SiO₂ particles are not vitrified or vitrified to a low degree. With the soot method, vitrification under formation of quartz glass takes place by subsequent sintering of the soot body. Through both methods, a dense, transparent, high-purity quartz glass is manufactured, while the manufacturing costs are lower with the soot method than with direct vitrification.

[0010] To reduce mechanical tensions within the blank and to evenly distribute the fictitious temperature, the blank is usually tempered. In EP-A 401 845, a tempering program is proposed in which the blank is submitted to a 50 hour holding period at a temperature of approximately 1100° C., is subsequently slowly cooled down to 900° C. with a cooling-down rate of 2°/h, and then cooled down to ambient temperature in the closed furnace. With this temperature treatment, the out-diffusion of components—above all hydrogen—can cause local changes to the chemical composition and result in a concentration gradient extending from the surface areas of the blank to its inside. To improve the radiation resistance of the quartz glass through the damage-healing effects of hydrogen, EP-A1 401 845 recommends a subsequent loading of the tempered quartz glass blank with hydrogen by treating it at increased temperature in a hydrogenous atmosphere.

[0011] In literature, a number of deterioration patterns are described where an increase of absorption occurred with continuing UV radiation. The induced absorption can show a linear increase, for example, or saturation is achieved after an initial increase. Furthermore, it is observed that an initially registered absorption band disappears some minutes after the laser has been switched off, only to rapidly re-establish itself on the level reached before at renewed radiation. This behavior is called “rapid damage process” (RDP). The background of this behavior is the fact that hydrogen molecules saturate the network defect sites in the quartz glass; however, the bonding strength at the defect sites is low such that the (the bonds break) defects will re-appear on renewed radiation of the component. Moreover, a damage behavior is known in which structural damages apparently cumulate to such a degree that there occurs a sudden sharp increase in absorption. The sharp increase in absorption with the damage behavior described last is called SAT effect in the literature.

[0012] In the quartz glass known from EP-A1 401 845, UV radiation causes a comparatively low increase in absorption, so that this quartz glass is characterized by a high resistance to short-wave UV radiation. Besides absorption and/or reduced transmission, however, other damaging mechanisms can take effect as well which may become evident in the generation of fluorescence or in a change of the refractive index.

[0013] A well-known phenomenon in this context is the so-called “compaction” which occurs during or after laser radiation with high energy density. This effect becomes apparent in a local increase of density resulting in an increase of the refractive index and thus to a deterioration of the imaging properties of the optical component. An effect to the contrary may occur as well, however, when an optical quartz glass component is exposed to laser radiation of low energy density and high pulse number. In these conditions, a so-called “de-compaction” is observed (also called “rarefaction” in literature), which is to be found together with a reduction of the refractive index. This results in a deterioration of the imagining properties. This damaging mechanism is described by C. K. Van Peski, R. Morton, and Z. Bor (“Behaviour of Fused Silica Irradiated by Low Level 193 nm Excimer Laser for Tens of Billions of Pulses”, J. Non-Cryst. Solids 265 (2000), p. 285-289).

[0014] Accordingly, compaction and de-compaction are defects or damages which do not necessarily become evident in an increase of the radiation-induced absorption but which can reduce the life of an optical component.

[0015] This invention is therefore based on the task to provide for a blank of synthetic quartz glass for an optical component for transmission of ultraviolet radiation of a wavelength of 250 nm and under, which has a low induced absorption while being optimized in respect of compaction and de-compaction. Furthermore, the invention is based on the task to provide for a suitable utilization for this blank.

[0016] Regarding the blank, this task is met according to the invention by an embodiment of a quartz glass blank in which the following properties are combined:

[0017] a glass structure which is essentially free of places with oxygen defect sites,

[0018] a content of H₂ ranging from 3×10¹⁷ molecules/cm³ to 2.0×10¹⁸ molecules/cm³,

[0019] an OH content ranging from 500 weight ppm to 1000 weight ppm;

[0020] a content of SiH groups of under 2×10¹⁷ molecules/cm³,

[0021] a chlorine content in the range of 60 weight ppm to 120 weight ppm,

[0022] a non-uniformity in the refractive index Δn of under 2 ppm, and

[0023] a stress birefringence of less than 2 nm/cm.

[0024] In this context, the glass structure being essentially free of oxygen defect sites shall mean a glass structure, in which the concentration of oxygen depletion defects and oxygen excess defects is below the detection limit of the method of Shelby. This detection method has been published: “Reaction of hydrogen with hydroxyl-free vitreous silica” (J. Appl. Phys., Vol. 51, No. 5 (May 1980), p. 2589-2593). In quantitative terms, this means that there are no more than approx. 10¹⁷ oxygen depletion defects and oxygen excess defects within the glass structure per gram of quartz glass.

[0025] Ideally, the stated ingredients and parameters are distributed homogeneously across the volume of the optical component. Here, the given concentration data refer to the optically utilized part (e.g. the irradiated volume) of the component.

[0026] The OH content is determined by measuring the IR absorption according to the method of D. M. Dodd et al. (“Optical Determinations of OH in Fused Silica”, J. Appl. Physics (1966), p. 3911). The H₂ content is determined by a Raman measurement which was first suggested by Khotimchenko et al. (“Determining the Content of Hydrogen Dissolved in Quartz Glass Using the Methods of Raman Scattering and Mass Spectrometry”, Zhurnal Prikladnoi Spektroskopii, vol. 46, no. 6 (June 1987), p. 987-991). The content of SiH groups is determined through Raman spectrometry, calibration taking place by means of a chemical reaction with hydrogen: Si—O—Si+H₂→Si—H+Si—OH, as described in Shelby (“Reaction of Hydrogen with OH-free Vitreous Silica”, J. Appl. Phys., vol. 51, no. 5 (May 1980), p. 2589-2593). The chlorine content of the quartz glass is determined chemically by means of precipitating chlorine as silver chloride, or by using an ion selective electrode.

[0027] The inhomogeneity of the refractive index, Δn, is determined by interferometry at a wavelength of 633 nm (He—Ne laser) with Δn being the difference between the maximal value and the minimal value of the refractive index distribution measured across the section of the optical component used for transmission, which is also called “clear aperture” area (CA area). The clear aperture area is determined by projection of the transmitting volume onto a plane perpendicular to the direction of transmission.

[0028] The stress birefringence is determined by interferometry at a wavelength of 633 nm (He—Ne laser) according to the method described in “Measurement of the residual birefringence distribution in glass laser disk by transverse Zeeman laser” (Electronics and Communications in Japan, Part 2, Vol. 74, No. 5, 1991; translated from Denshi Joho Tsushin Gakkai Ronbunshi Vol. 73-C-I, No. 10, 1990, p. 652-657).

[0029] Contrary to the quartz glass qualities described in prior literature which are designed in view of high radiation resistance to short-wave UV radiation, the quartz glass of the blank according to the invention is characterized, among other features, by relatively high H₂ and OH contents on the one hand, and on the other hand by a chlorine content with a comparably narrow range of concentration between 60 weight ppm and 120 weight ppm.

[0030] The manufacture of such quartz glass through the “soot method” described above is not without problems, because the quartz glass manufactured through the soot method usually has an OH content ranging from a minor number of weight ppm to 200 weight ppm, the H₂ content typically being below the detectability limit as a consequence of the temperature treatments on vitrification and homogenization of the quartz glass. Quartz glass manufactured by direct vitrification, on the contrary, typically shows OH contents from. 450 to 1200 weight ppm and OH contents of approximately 1×10¹⁸ molecules/cm³. It is surprising to find that with such a quartz glass, chlorine has a positive effect on radiation resistance if it is present in a narrow concentration range between 60 weight ppm to 120 weight ppm. With a chlorine content of more than 120 weight ppm, an increase of induced absorption due to the interference of chlorine radicals in the generation of defect centers is observed (SiOSi+Cl*→SiCl+SiO*→(H₂+hv)SiOH+SiH+Cl*), while a chlorine content of less than 60 weight ppm has negative effects on the de-compaction behavior.

[0031] It has shown that in an optical component manufactured from a quartz glass blank of the above described properties, the damaging mechanisms resulting in compaction and de-compaction can be avoided or at least significantly reduced. In the course of the intended use of such components, changes to the refractive index are avoided completely or to a large degree, so that the named damaging mechanisms will not limit the life of the optical components manufactured from the blank according to the invention.

[0032] This effect of the above mentioned combination of properties on the damaging behavior in respect of short-wave UV radiation with energy densities of more than 0.05 mJ/cm² has been empirically evidenced, as will be explained in detail in the following. In this connection, it has also become evident that with these energy densities, OH contents of under 500 weight ppm lead to compaction. Quartz glass with an OH content of more than 1000 weight ppm shows a more pronounced tendency to de-compaction.

[0033] With H₂ contents of more than 2.0×10¹⁸ molecules/cm³, the damaging mechanism leading to RDP takes especially significant effect. With an H₂ content of less than 3×10¹⁷ molecules/cm³, however, the above damage-healing function of hydrogen in relation to short-wave UV radiation with energy densities exceeding 0.05 mJ/cm² is so small that there occur intolerable transmission losses during the intended use of the optical component.

[0034] In contrast, the quartz glass of the blank according to the invention is optimized in respect of compaction as well as de-compaction, simultaneously showing little induced absorption towards short-wave UV radiation.

[0035] It has proved to be especially advantageous when the OH content in the blank is in the range of 600 weight ppm to 900 weight ppm, and especially between 750 weight ppm and 900 weight ppm. An OH content in this range is a preferable compromise between de-compaction and compaction on the one hand, and RDP on the other hand, if the quartz glass is to be used with energy densities of more than 0.05 mJ/cm².

[0036] In this respect, the H₂ content is advantageously in a range of 5×10¹⁷ molecules/cm³ to 1×10¹⁸ molecules/cm³. With a quartz glass blank having an H₂ content in this range, the favorable, damage-healing function of hydrogen is present to an especially high degree, de-compaction being largely avoided at the same time.

[0037] Preferably, the quartz glass blank has a chlorine content in a range of 80 weight ppm to 100 weight ppm. With a chlorine content within these narrow concentration limits, low de-compaction and induced absorption is achieved, above all when the quartz glass blank is used in connection with UV radiation of high energy densities of more than 0.05 mJ/cm².

[0038] In view of the utilization of the quartz glass blank, the above task is met by the invention by selecting for use with ultraviolet radiation of a given pulse energy density ε of 0.05 mJ/cm² as a minimum and for a given pulse number P, a quartz glass having a minimum hydrogen content C_(H2min) and a maximum hydrogen content C_(H2max) in accordance with the following scaling laws:

C _(H2min) [molecules/cm³]=1.0×10⁸ε² P  (2), and

C _(H2max) [molecules/cm³]=2×10¹⁹ε  (3).

[0039] (ε in mJ/cm³)

[0040] By adjusting the hydrogen content according to the scaling laws (2) and (3), the quartz glass is further optimized in respect of its damage behavior towards short-wave UV radiation. From scaling law (2), there follows a minimum hydrogen concentration in dependence on the radiation conditions (pulse energy density and pulse number) below which the defect-healing function of hydrogen is so little that there occur intolerable transmission losses during the intended use of the optical component. Scaling law (3) defines an upper limit of hydrogen in dependence of the pulse energy density, above which there occurs RDP and/or de-compaction to an increased degree. The given hydrogen concentrations refer in each case to the area within the quartz glass blank (CA area) used for transmission. Usually, this is the center area of the component, respectively the quartz glass blank.

[0041] Preferably, a quartz glass is selected having an OH content C_(OH) in a range meeting the following scaling law:

C _(OH) [weight ppm]=1700ε [mJ/cm²]^(0.4)±50  (4)

[0042] Ideally, there will be neither compaction nor de-compaction. In practice, however, either compaction or de-compaction is observed in dependence on the radiation conditions and the properties of the quartz glass. Surprisingly, it was found that a quartz glass with an OH content according to scaling law (4) comes close to the described ideal, that is to say, it shows neither conspicuous compaction nor significant de-compaction on exposure to short-wave UV radiation of a wave length of <250 nm with a pulse energy density ε of more than 0.05 mJ/cm².

[0043] For a pulse energy density in the range of the above named lower limit ε=0.05 mJ/cm², scaling law (4) results in an OH content of 513 weight ppm.

[0044] The scaling law (4) has proved to be valuable above all for the determination of the OH content in view of low compaction and simultaneously low de-compaction with a pulse energy density of under 0.3 mJ/cm², preferably under 0.15 mJ/cm².

[0045] For the upper limit ε=0.3 mJ/cm², the OH content according to the scaling law (4) is between 1000 weight ppm and 1100 weight ppm.

[0046] In the following, the invention is explained in details by way of embodiments and a drawing. It is shown in

[0047]FIG. 1 a diagram for explanation of the occurrence of compaction or de-compaction in dependence on the OH content of the quartz glass and the pulse energy density of the radiation.

[0048] In the diagram in FIG. 1, the OH content C_(OH) in weight ppm (in the Figure, given as “OH content” outlined against the pulse energy density ε in mJ/cm² (in the Figure, given as “energy density”). The shown curve is based on damages measured in various quartz glass qualities with different OH contents. The measurements were taken under laser radiation of a wave length of 193 nm and with a laser pulse duration between 20 and 50 nanoseconds. The laser pulse duration is defined according to the method described in V. Liberman, M. Rothschild, J. H. C. Sedlacek, R. S. Uttaro, A. Grenville “Excimer-Laser-Induced Densification of Fused Silica: Laser-Fluence and Material-Grade Effects on Scaling Law”, Journal Non-Cryst. Solids 244 (1999), p. 159-171.

[0049] The measured values determined under the named conditions are depicted in rhombic shape. The curve represents those C_(OH)/ε pairs in which neither compaction nor de-compaction is observed. The area (1) above the curve stands for the area where compaction occurs, and the area (2) below the curve stands for the area where de-compaction occurs.

[0050] The approximate course of the curve can be described by the formula (4):

C _(OH) [weight ppm]=1700ε [mJ/cm²]^(0.4)±50  (4)

[0051] Accordingly, by means of the curve or the formula (4), it is possible to select for every pulse energy density between 0.05 and 0.3 mJ/cm³ the OH content required by a quartz glass to show neither compaction nor de-compaction.

[0052] In Table 1, examples for such quartz glasses and examples for comparison are given. TABLE 1 2 3 4 OH H₂ Cl 5 content content content SiH groups 6 7 8 9 11 12 1 [weight [molecule [weight [molecules/ O^(±) Δn Λ ε 10 De- Induced No. ppm] s/cm³] ppm] cm³] [g⁻¹] [ppm] [nm/cm] [mJ/cm²] Compaction compaction absorption 1 700 1 × 10¹⁸ 90   7 × 10¹⁶ <10¹⁷ <2 <2 0.1 no no no 2 700 1 × 10¹⁸ 90   7 × 10¹⁶ <10¹⁷ <2 <2 0.3 yes no no 3 700 1 × 10¹⁸ 30   7 × 10¹⁶ <10¹⁷ <2 <2 0.1 no yes no 4 700 1 × 10¹⁸ 200   7 × 10¹⁶ <10¹⁷ <2 <2 0.1 no no yes 5 880 5 × 10¹⁷ 90 <5× 10¹⁶ <10¹⁷ <2 <2 0.2 no no no 6 880 5 × 10¹⁷ 90 <5× 10¹⁶ <10¹⁷ <2 <2 0.05 no yes no 7 500 5 × 10¹⁷ 90 <5× 10¹⁶ <10¹⁷ <2 <2 0.05 no no no

[0053] Table 1 shows the results of the radiation measurements at quartz glass blanks of various chemical composition and with various irradiation conditions. In the three last columns of the table, it is shown in terms of quality whether the respective blank shows compaction, de-compaction or induced absorption.

[0054] The properties named in columns 2 to 8 are determined at one cylindrical quartz glass blank with an outside diameter of 240 mm and a thickness of 60 mm, such blanks being intended to be used as lenses for a microlithography device operating with excimer laser radiation with a wave length of 193 nm. Apart from a slight excess which remains to be removed on manufacturing the lens, the blank dimensions correspond to the lens dimensions. Here, the quartz glass volume corresponding to the CA area of the lens manufactured from it is defined by the circular area of the lens—minus a border of some millimeters for the mount of the lens—and by the thickness of the lens. In the column “O^(±)” of Table 1, the concentration of places with oxygen damages is given, in the column “Δn” the refractive index determined through the CA area, and in the column “Λ” the maximum birefringence determined in the CA area.

[0055] For the radiation tests, bar-shaped samples of 25×25×200 mm³ were taken from the respective quartz glass blank and prepared identically (polishing of the opposite 25×25 mm² areas).

[0056] To clarify the damage behavior of the samples in respect of compaction or de-compaction, the samples were submitted to UV radiation of a wave length of 193 nm, with varying pulse energy densities, as given in column 8 of Table 1. The pulse number was 5 billion in each of these irradiation tests.

[0057] In the column “Induced absorption”, two damage mechanisms are combined which become evident in an increase of absorption, that is to say linear increase of absorption, and the RDP described in the beginning. To clarify the damage behavior of the samples in respect of induced absorption, the samples were likewise submitted to UV irradiation of a wave length of 193 nm and the pulse energy density given in column 8. To determine the RDP, a pulse number of 1 million pulses is sufficient, the determination of the linear increase in absorption requiring a minimum pulse number of 1 billion pulses. For this purpose, the transmission loss of the sample is determined by defining during radiation the loss of intensity of the utilized laser beam after passing through the sample.

[0058] After the irradiation tests, compaction and de-compaction were defined by measuring the relative increase or reduction of the refractive index in the radiated area in comparison to the non-radiated area through a commercially available interferometer (Zygo GPI-XP) at a wave length of 633 nm.

[0059] The quartz glass blanks are designed for the manufacture of optical lenses for a microlithography unit for use with UV radiation of a wave length of 193 nm, the optical component during its intended use being typically exposed to radiation at an energy density of approx. 0.1 mJ/cm². The typical pulse numbers are between 10¹¹ and 10¹².

[0060] The blanks 1 to 4 according to Table 1 were manufactured as follows:

[0061] They are quartz glasses manufactured through the direct vitrification method. On a discoid substrate rotating around its central axis, fine-particle SiO₂ is precipitated by means of an oxyhydrogen burner, which SiO₂ is vitrified directly through the heat of the oxyhydrogen flame under formation of a bar-shaped quartz glass blank. In this process step, the hydrogen content is still approximately 2×10¹⁸ molecules/cm³.

[0062] As can be seen from Table 1, the blanks 1 to 4 differ only in their chlorine contents. The Cl content is adjusted by setting the flow rates for H₂, O₂ and SiCl₄.

[0063] Furthermore, according to scaling law (4,) the OH content is determined which is to be set in connection with the typical pulse energy density in use, i.e. approx. 0.1 mJ/cm². The OH content is likewise set via the flow rates of the individual media (H₂, O₂ and SiCl₄). This results in an OH content of approx. 700 weight ppm, which thus is within a range specified by scaling law (4) for ε=0.1 mJ/cm² as follows:

C _(OH) [weight ppm]=1700ε [mJ/cm²]^(0.4)±50 →677±50 weight ppm

[0064] Furthermore, the hydrogen content is determined according to scaling laws (2) and (3) in correspondence to the settings required with the typical pulse energy density in use, i.e. approx. 0.1 mJ/cm². The set H₂ content is adjusted by tempering the blanks at 1100° C.

[0065] This results in an H₂ content of 1.4×10¹⁸ molecules/cm³, which—under consideration of the out-diffusion during tempering the hot-formed lens blank (see below) (H₂ loss by out-diffusion approx. 30%)—is within the limits C_(H2min) and C_(H2max) which are specified as follows by the scaling laws (2) and (3) for ε=0.1 mJ/cm²:

C _(H2min) [molecules/cm³]=1.0×10⁸(0.1)² P

C _(H2max) [molecules/cm³]=2.0×10¹⁹(0.1)

[0066] According to this scaling law, and with ε=0.1 mJ/cm², the minimum H₂ content to be set in the quartz glass is determined as—depending on the pulse number—1×10¹⁷ molecules/cm³ and 10×10¹⁷ molecules/cm³, and the maximum H₂ content is determined as 2×10⁸ molecules.

[0067] For homogenizing, the quartz glass blank is then clamped into a quartz glass lathe, heated in zones to a temperature of approx. 2000° C., and twisted. A suitable homogenizing method is described in EP-A1 673 888. After repeated twisting, a quartz glass body in the form of a round bar of a diameter of 80 mm and a length of approx. 800 mm is realized which is free of striae in three directions.

[0068] By hot-forming at a temperature of approx. 1700° C. and using a nitrogen-flushed casting mold, a circular quartz glass cylinder with an outside diameter of 240 mm and a length of 80 mm is formed from the above quartz glass body. After another tempering process in which the quartz glass cylinder is heated to 1100° C. under air and atmospheric pressure and subsequently cooled to 900° C. at a cooling rate of 2° C./h, a stress birefringence (in the CA area) of a maximum of only 2 nm/cm is measured, and the distribution of the refractive index is so homogeneous that the difference between the maximum and the minimum value is under 2×10⁻⁶. From the center of the blank, a bar-shaped sample of 25×25×200 mm³ is taken, having an H₂ content of approx. 1×10¹⁸ molecules/cm³ and approx. 700 weight ppm OH. As the blanks 1-4, the blanks 5-7 are manufactured by varying the flow rates of the individual media. The H₂ content of the resulting blanks is set by selecting the duration of the tempering program, and under consideration of the diffusion of tempering the heat-formed quartz glass cylinder.

[0069] Evaluation of the Result

[0070] Regarding the occurrence of compaction, de-compaction and induced absorption according to Table 1, the blanks 1, 5, and 7 with energy densities of 0.1, 0.2 or 0.05 mJ/cm² show the best results. Blank 2 shows compaction under influence of ultraviolet radiation with a relatively high energy density of 0.3 mJ/cm², which may be tolerable within certain limits in individual cases. 

1. A quartz glass blank for an optical component for transmission of ultraviolet radiation of a wave length of 250 nm and under, having a glass structure which is essentially free of oxygen defect sites, an H₂ content in the range of 3×10¹⁷ molecules/cm³ to 2.0×10¹⁸ molecules/cm³, an OH content in the range of 500 weight ppm to 1000 weight ppm, an SiH group content of less than 2×10¹⁷ molecules/cm³, a chlorine content in the range of 60 weight ppm to 120 weight ppm, a non-homogeneity in the refractive index Δn of less than 2 ppm, and a stress birefringence of less than 2 nm/cm.
 2. A quartz glass blank according to claim 1, characterized in that the OH content is in the range of 600 weight ppm to 900 weight ppm, preferably in the range of 750 weight ppm to 900 weight ppm.
 3. A quartz glass blank according to claim 1 or 2, characterized in that the H₂ content is in the range of 5×10¹⁷ molecules/cm³ to 1×10¹⁸ molecules/cm³.
 4. A quartz glass blank according to claim 1, characterized in that the quartz glass blank has a chlorine content is in the range of 80 weight ppm to 100 weight ppm.
 5. The utilization of a quartz glass blank according to any of the claims 1 to 4 for manufacture of a component to be used in microlithography in connection with ultraviolet radiation of a wave length of 250 nm and under, characterized in that for the use with ultraviolet radiation of a given pulse energy density ε of at least 0.05 mJ/cm² and for a given pulse number P, a quartz glass is selected having a minimum hydrogen content C_(H2min) and a maximum hydrogen content C_(H2max) which are in accordance with the following scaling laws: C _(H2min) [molecules/cm³]=1.0×10⁸ε² P  (2), and C _(H2max) [molecules/cm³]=2×10¹⁹ε  (3).
 6. The utilization of a quartz blank according to claim 5, characterized in that a quartz glass blank is selected having an OH content C_(OH) which is in accordance with the following scaling law: C _(OH) [weight ppm]=1700ε [mJ/cm²]^(0.4)±50  (4)
 7. The utilization of a quartz glass blank according to claim 5, characterized in that the pulse energy density ε is under 0.3 mJ/cm², and especially smaller than 0.15 mJ/cm². 